1. Field of the Invention
The present general inventive concept relates to an inkjet image forming device, and more particularly, to a method and apparatus to compensate for a degradation of image quality generated by a defective nozzle of the inkjet image forming device.
2. Description of the Related Art
In general, inkjet image forming devices are devices used to form images by ejecting ink from a printer head moving in a direction perpendicular to a feeding direction of a print medium and being separated from the print medium by a predetermined distance. Such an image forming device printing images by ejecting ink onto a print medium while moving in the direction perpendicular to the feeding direction of the print medium is referred to as a shuttle inkjet image forming device. A printer head used in shuttle inkjet image forming devices includes a nozzle module containing a plurality of nozzles for ejecting ink.
Recently, high-speed printing has been performed using printer heads having a nozzle module of a length equal to a width of the print medium instead of using a printer head which shuttles in the width direction of the print medium. An image forming device using this method is referred to as a line printing inkjet image forming device. In the line printing inkjet image forming device, the printer head is fixed, and only the print medium is fed (i.e., only the print medium moves). Thus, a driving apparatus of the line printing inkjet image forming device is simpler, and as a result, higher-speed printing can be realized.
FIG. 1 is a diagram illustrating a print pattern obtained when a defective nozzle is included in a nozzle module of a conventional line printing inkjet image forming device, and FIGS. 2A through 2D are diagrams illustrating a process of compensating for the defective nozzle included in the conventional line printing inkjet image forming device illustrated in FIG. 1.
Referring to FIG. 1, the conventional line printing inkjet image forming device prints an image by ejecting ink I from a plurality of nozzles 82 included in a nozzle module 80. When a specific nozzle 84 of the nozzle module 80 is damaged (i.e., a defective nozzle 84), a line corresponding to the defective nozzle 84 is not printed on the print medium, as illustrated in FIG. 1, since the ink I is not properly ejected onto a print medium from the defective nozzle 84. That is, when a portion of the plurality of nozzles 82 is damaged, since the ink I is not ejected onto a portion of the print medium corresponding to the defective nozzle 84, a white band, such as a missing line, occurs in the print image printed on the print medium. Since the white band in the print image printed on the print medium is easily recognized, the white band significantly affects print quality. A conventional method of compensating for a degradation of image quality due to a defective nozzle, as illustrated in FIGS. 2A through 2D, is disclosed in U.S. Pat. No. 5,581,284.
Specifically, when a defective nozzle is present in an inkjet image forming device, the conventional method disclosed in U.S. Pat. No. 5,581,284 can be used to compensate for the defective nozzle. Here, the defective nozzle is a nozzle which cannot normally eject ink, such as a missing nozzle which cannot eject ink or a weak nozzle whose ejection function has become weakened. According to U.S. Pat. No. 5,581,284, if a defective nozzle 63 (see FIG. 2A) of a mono, i.e., black, color is detected, and if the defective nozzle 63 must be used, other colors, i.e., cyan, magenta, and yellow, are sequentially printed in an area in which the defective nozzle 63 should print. These procedures are illustrated in FIGS. 2B, 2C, and 2D. If cyan, magenta, and yellow are printed on the same location corresponding to the defective nozzle, a black color can be generated to compensate for a defective black nozzle. This black color generated by printing cyan, magenta, and yellow on the same location is referred to as process black or composite black. However, this method cannot be used when a nozzle ejecting a color other than black (e.g., cyan, magenta, or yellow) is damaged. In addition, when any one of three nozzles (e.g., one of a cyan nozzle, a magenta nozzle, or a yellow nozzle) used to compensate for the defective black nozzle (i.e., by printing cyan, magenta, and yellow on the same location) is also damaged, an undesired color is printed, such as red (yellow+magenta, when the cyan nozzle is also defective), green (cyan+yellow, when the magenta nozzle is also defective), or blue (cyan+magenta, when the yellow nozzle is also defective), which contrasts strongly with process black, thereby significantly affecting print image quality. Thus, it is necessary to improve the image quality by compensating for the defective nozzle.